CN114503791A

CN114503791A - Laser soldering method and laser soldering apparatus

Info

Publication number: CN114503791A
Application number: CN201980100692.8A
Authority: CN
Inventors: 渡边信次
Original assignee: OMC Co ltd
Current assignee: OMC Co ltd
Priority date: 2019-09-26
Filing date: 2019-09-26
Publication date: 2022-05-13
Also published as: KR102496836B1; KR20220053039A; EP4013196A4; TWI740428B; JPWO2021059456A1; JP6744686B1; EP4013196A1; TW202112478A; WO2021059456A1; US20220320811A1

Abstract

Hot air (N) is sprayed from below the printed board (40) to the bonding pad (42) and the lead (52) for preheating. After the start of preheating or after the start of preheating, the laser beam (L) is irradiated to the soldering point and the solder wire (15) is supplied to a position where the solder wire is in contact with the soldering point. The supplied soft solder wire (15) is melted by a laser (L). After the soldering is completed, the supply of the solder wire (15) is stopped. The irradiation of the laser (L) is stopped to solidify the molten solder (15 m).

Description

Laser soldering method and laser soldering apparatus

Technical Field

The present invention relates to a laser soldering method for soldering using a laser and a laser soldering apparatus for carrying out the method.

Background

In general, reflow soldering is often used for mass production and mounting of electronic components. Typical reflow soldering uses the following method: after the leads of the electronic component are arranged on the lands of the printed board coated with the paste-like solder, the solder is melted by passing the solder through a reflow furnace, and the leads of the electronic component and the corresponding lands on the printed board are joined by soldering.

In such reflow soldering, the printed circuit board is heated in a reflow furnace, and therefore, there is a problem that thermal strain or deformation occurs.

Therefore, recently, attention has been paid to a system in which such a reflow method is replaced with a laser soldering method.

In a conventional laser soldering apparatus, an electronic component is mounted on an upper surface of a printed circuit board to be soldered, and a laser beam is irradiated from an injection head provided above the printed circuit board to a solder joint (a pad and a lead) exposed between the electronic component. Solder wires are fed into the soldering points. The solder wire reaching the laser irradiation region is sequentially melted, and the melted solder drops to adhere to the pad and the lead on the upper surface side of the printed circuit board, flows downward in the gap between the pad and the lead, and bypasses to the lower surface side of the printed circuit board. Then, the solder is solidified to form a complete conical solder layer centering on the lead on both the upper and lower surfaces of the printed circuit board.

Laser soldering can perform noncontact and local soldering by condensing and irradiating a laser beam onto a fine portion, and can avoid thermal strain of a printed circuit board. In addition, the method is also beneficial to automation of soldering operation.

However, with further high integration of the printed circuit board, a space between the electronic components cannot be obtained, and the laser cannot be irradiated from the upper surface side of the printed circuit board on which the electronic components are mounted as in the conventional case.

Therefore, as shown in patent document 1, a technique has been proposed in which a printed circuit board is turned upside down so that the mounting surface of an electronic component faces downward, and soldering is performed by supplying a solder wire to a lead of the electronic component extending upward from a through hole of the printed circuit board and a pad of the through hole and irradiating laser light from above the printed circuit board.

Prior art documents

Patent document

Patent document 1: japanese patent laid-open publication No. 2013-187411

Disclosure of Invention

Problems to be solved by the invention

However, if the printed circuit board is turned upside down and the electronic component is disposed on the lower surface side, the electronic component drops in this state, and therefore, some jigs are necessary to fix the mounted electronic component to the printed circuit board while maintaining the positional relationship during the turning, which complicates the soldering operation.

Before soldering, it is necessary to preheat a pad or a lead serving as a solder point to a temperature near the melting temperature of the solder. In a state where a pad or a lead of an electronic component is cooled without being preheated, a solder melted by a laser beam is immediately solidified when contacting the lead or the pad in a cooled state, and adhesion is impaired, thereby causing solder failure.

However, when the solder spot is irradiated with laser light for the preheating, if the output of the laser light is increased for melting the preheated solder wire, the lead wire is overheated and discolored, which is referred to as "lead burn".

Therefore, in patent document 1, the pad on the irradiation side is divided into a first pad including a through hole for fixing a lead by soldering and a second pad provided at a position extending from the first pad and allowing molten solder to flow into the first pad, and the irradiation state by the laser is divided into a first irradiation state in which only the second pad is irradiated with the laser and a second irradiation state in which the first pad is irradiated with the laser, and the two states can be switched.

In this method, a space for providing the second pad extending from the first pad is necessary, but in the printed circuit board in the above-described dense state, the space for providing the second pad cannot be provided, though on the lower surface side. Further, not only is the operation of dividing the irradiation state into the first irradiation state and the second irradiation state and switching them as described above and causing the molten solder at the second pad to flow into the first pad complicated, but also the first pad and the lead wire have to be preheated from that time by the laser for soldering, and the tact time of the operation is extended.

Therefore, the inventors considered the following method: a solder wire is supplied obliquely upward from below toward a solder point (a pad on the lower surface side and a lead protruding from the pad) on the lower surface side of the printed circuit board, and the portion is irradiated with a laser beam. However, in this method, it is generally considered as follows: first, fumes generated during soldering or fine particles (solder beads) ejected from the surface of the solder during melting of the solder fall down to adhere to a protective glass provided on a laser emission window of an emission head provided below a printed board, thereby rapidly contaminating the glass.

The present invention has been made in view of the above problems, and an object thereof is to develop a laser soldering method and a laser soldering apparatus which are capable of performing soldering from below a printed circuit board, which has been considered impossible in the past, and which are capable of shortening the tact time of a soldering operation as much as possible in a highly integrated printed circuit board.

Means for solving the problems

In order to solve the above problem, the present invention emits laser light L from the lower side of the printed board 40. Accordingly, a countermeasure for eliminating the problem is also taken. The emission angle is determined by both the case of emitting light perpendicularly toward the lower surface 40k of the printed circuit board 40 (fig. 1 to 8) and the case of emitting light obliquely (fig. 11 to 12). As the laser light L to be emitted, laser light having the same output level (hereinafter, referred to as uniform output level, and this laser light is referred to as uniform output laser light) over the entire cross section of the irradiation surface as shown in fig. 9 a, and laser light having different output levels (hereinafter, referred to as non-uniform output level, and this laser light is referred to as non-uniform output laser light) at the center portion and the outer peripheral portion as shown in fig. 10 a are used. Further, various methods are adopted for the output step.

The laser soldering method according to the present invention (first invention) is a laser soldering method for melting a solder wire 15 supplied to a through hole 41 of a printed board 40 by a laser L and soldering a lead 52 inserted through the through hole 41 of an electronic component 50 mounted on an upper surface 40j side of the printed board 40 to a pad 42 provided in the through hole 41,

the laser light L is irradiated perpendicularly or obliquely from below with respect to the pad 42 at the soldering point P,

hot air N is sprayed from below the printed circuit board 40 to the pad 42 and the lead 52 protruding downward from the through hole 41 to preheat the pad 42 and the lead 52,

simultaneously with or after the start of the preheating, the solder wire 15 is supplied from below the printed board 40 to a position in contact with either the pad 42 or the lead 52 while irradiating the pad 42 and the lead 52 with laser light from below the printed board 40,

then, the supplied solder wire 15 is melted by the laser L, the pad 42 and the lead 52 are connected by the melted solder 15m,

then, the supply of the solder wire 15 is stopped, and at the same time as or after the stop of the supply of the solder wire 15, the irradiation of the laser light L is stopped to solidify the molten solder 15 m.

Claim 2 in the above soldering method, preheating (1), (2), (3) and soldering step (4) in the first output step are employed using the laser light L of uniform output shown in fig. 9 (b).

The laser soldering method according to claim 1, wherein the solder layer is formed by a laser soldering method,

using the laser light L whose output level is equal over the entire cross section of the irradiation face,

the output level during preheating is set to a preheating level (A) below the melting temperature of the solder wire 15,

the output level during soldering is set to a melting level (B) equal to or higher than the melting temperature of the solder wire 15.

Claim 3 in the above soldering method, preheating (10) and soldering step (4) in the second output step are employed using the laser light L of uniform output shown in fig. 9 (b).

preheating is performed based only on the hot wind N at the time of preheating,

at the start of soldering, laser light L is emitted so that the output level thereof becomes a melting level (B) equal to or higher than the melting temperature of solder wire 15.

Claim 4 in the above soldering method, the preheating (20) and the soldering step (4) in the third output step are employed using the laser light L of uniform output shown in fig. 9 (b).

laser L is emitted at the beginning of or during the preheating to gradually increase the output level from zero to a melting level (B) above the melting temperature of the solder wire 15,

Claim 5 the above-mentioned soldering method uses the laser light L of unequal output as shown in fig. 10(b) and adopts the preheating (1), (2), (3) and the soldering step (4) in the first output step.

using a laser light L whose output level of the cross section of the irradiated face is higher at its outer peripheral portion L2 than at its central portion L1,

the output level (a) of said central portion L1 is lower than the melting temperature of the solder wire 15,

the output level (B) of the outer peripheral portion L2 is higher than the melting temperature of solder wire 15,

the central portion L1 is set to irradiate the inside of the through hole 41 of the pad 42,

Claim 6 the above soldering method uses the laser light L of uneven output shown in fig. 10(b) and adopts the preheating (10) and soldering step (4) of the second output step.

using the laser light L whose output level of the entire cross section of the irradiated face is higher at its outer peripheral portion L2 than at its central portion L1,

preheating is performed based only on the hot wind N at the time of preheating,

when the soldering is started, the laser beam L is emitted so that the output level thereof becomes the melting level (B) equal to or higher than the melting temperature of the solder wire 15.

Claim 7 is a method of soldering in which the laser light L of an unequal output shown in FIG. 10(b) is used, and preheating (20) and soldering (4) are employed in a third output step.

Claim 8 is an apparatus for executing the soldering method described in claims 1 to 7.

A laser soldering apparatus 1 for soldering a lead 52 of an electronic component 50 to a pad 42 of a printed board 40 by a laser L,

the laser soldering apparatus 1 includes:

a support base 2 for supporting a printed board 40, the electronic component 50 being mounted on an upper surface 40j of the printed board 40, the lead 52 of the electronic component 50 protruding downward from a through hole 41 of the printed board 40;

an ejection head 3 which is provided below the printed board 40 so as to be perpendicular to or inclined with respect to the printed board 40 and which ejects a laser beam L toward the pad 42 so as to be perpendicular to or inclined with respect thereto;

a solder wire feeder 11 for feeding a solder wire 15 to a position where the solder wire contacts either the pad 42 or the lead 52 during soldering;

a hollow protection nozzle 20 provided in the injection port 4 of the injection head 3, extending upward from the injection port 4 toward the printed board 40, and having a through hole 22 provided at a distal end facing the printed board 40; and

and a heated gas supply pipe 26 provided in the protective nozzle 20, for supplying a heated gas to the protective nozzle 20 to eject the hot air N from the through hole 22 toward the printed circuit board 40.

The laser soldering apparatus 1 according to claim 8, wherein an exhaust duct 30 is further provided in claim 9, and the exhaust duct 30 collects the hot air N discharged from the protective nozzle 20 together with the scattered fine products C generated during soldering, and the exhaust duct 30 is further provided in a position facing the through hole 22 of the protective nozzle 20, and an upper surface of the exhaust duct 30 facing the lower surface 40k of the printed circuit board 40 is open.

Claim 10 the laser light L according to claim 8, wherein,

using a laser light L having an equal output level of the entire cross section of the irradiation surface, or a double ring configuration formed of a center portion L1 of the cross section of the irradiation surface and an outer peripheral portion L2 surrounding the center portion L1, the output level (a) of the center portion L1 is set to be equal to or lower than the melting temperature of the solder wire and the output level (B) of the outer peripheral portion L2 is set to be equal to or higher than the melting temperature of the solder wire.

Claim 11 is the protection nozzle 20 according to claim 8, characterized in that,

the protective nozzle 20 is formed so as to be reduced in diameter toward the through hole 22,

inside the protection nozzle 20, a guide wall 24 for guiding hot air is provided along an inner circumferential surface of the protection nozzle 20.

ADVANTAGEOUS EFFECTS OF INVENTION

The present invention, having the above-described configuration, can perform soldering from below the printed board 40, which has been considered impossible in the past. In addition, in the present invention, since the solder joints P are preheated by the hot air N and the laser beam L is irradiated perpendicularly to the printed circuit board 40 without moving or obliquely upward from obliquely downward to obliquely upward, the tact time of the soldering operation can be shortened as much as possible in the ultra-high integrated printed circuit board 40. Moreover, by conducting research on the output step or the laser L, burn of the lead of the electronic part 50 can also be avoided.

Drawings

FIG. 1 is a cross-sectional view showing one embodiment of a laser soldering apparatus under vertical irradiation according to the present invention.

Fig. 2 is an enlarged cross-sectional view of the protective nozzle portion of fig. 1.

Fig. 3 is an enlarged partially sectional perspective view of fig. 1 as viewed from below.

Fig. 4 is an X-X sectional view of fig. 2.

FIG. 5 is a perspective view of the present invention at the start of soldering.

FIG. 6 is a perspective view of the present invention during soldering.

FIG. 7 is an enlarged sectional view of the soldered state in FIG. 6.

FIG. 8 is a perspective view of the present invention at the time of post-heating after soldering is completed.

Fig. 9 is an output control diagram of the laser in the first method of the present invention.

Fig. 10 is an output control diagram of the laser in the second method of the present invention.

Fig. 11 is a partially enlarged cross-sectional view under oblique irradiation of the present invention.

Fig. 12 is an enlarged view of the lower surface side of the printed board showing the state of irradiation at the soldering point in fig. 11.

Detailed Description

The present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a first embodiment (vertical irradiation) of a soldering apparatus 1, and FIG. 11 shows a second embodiment (oblique irradiation). In the description of the second embodiment, the description will be mainly given of the portions different from the first embodiment, and the description of the same portions will be applied to the description of the second embodiment, and the description of the portions will be omitted.

The soldering device 1 includes: a semiconductor laser or a laser oscillator (not shown) for outputting laser light L; a support table 2 on which the printed substrate 40 is placed; an injection head 3 provided below the printed circuit board 40 and configured to irradiate a solder spot (a portion on the lower surface side of the land 42 of the printed circuit board 40 in the present invention, which is a lower surface portion 42k of the land) provided on the lower surface 40k of the printed circuit board 40 with laser light L output from a semiconductor laser or the like; a laser controller (not shown) for controlling the semiconductor laser and the like; a solder wire supply unit 11 for supplying a solder wire 15 to the solder joints; a monitor 10 for displaying the state of the solder; and a control device (not shown) for automatically controlling the entire soldering apparatus 1 in accordance with a set program.

The printed board 40 is a board for mounting a plurality of electronic components 50. The printed board 40 is not limited to 1 layer, and there are multilayer printed boards, but a typical example thereof will be described here as a 1-layer printed board.

A plurality of through holes are formed in a substrate body (insulating substrate) 40a of the printed substrate 40 so as to penetrate from the upper surface 40j to the lower surface 40k thereof. A copper plating layer remaining by etching treatment is present on the inner peripheral surface of the through-hole and the periphery of the opening of the through-hole on the front and back sides of the substrate main body 40 a. The portion of the copper plating layer is a pad 42, and the hole through the pad 42 is a via hole 41.

The annular copper plating layer on the periphery of the opening of the pad 42 is defined as a pad upper surface portion 42j and a pad lower surface portion 42k, and the copper plating layer on the inner peripheral surface of the through hole connecting the pad upper surface portion 42j and the pad lower surface portion 42k on the front and back sides is defined as a conductive portion 43.

A plurality of electronic components 50 of plural types are mounted on the upper surface 40j of the printed board 40, and their leads 52 are inserted into the through holes 41. The inserted leads 52 extend through the through-holes 41 and protrude slightly beyond the lower surface 40 k. The inserted lead 52 is soldered to the entire pad 42 of the printed board 40 by a method described later. The lead 52 is adapted to various electronic components 50, and includes various leads such as a lead having a circular cross section and a lead having a quadrangular cross section.

In the present invention, the laser L irradiates the protruding lead 52 and the pad lower surface portion 42k on the lower surface 40k side of the printed board 40 from which the inserted lead 52 protrudes, melts the solder wire 15 supplied to the portion, and solders the lead 52 and the pad 42 (fig. 8).

The copper plating layer (conductive portion 43) as the inner peripheral portion of the pad 42 and the lead 52 of the electronic component 50 are in a relationship such that the diameter of the lead 52 is slightly smaller than the inner diameter of the conductive portion 43, the gap S between the conductive portion 43 and the lead 52 is small (for example, about 0.1 mm), and the molten solder 15m is a gap into which the capillary phenomenon can penetrate as described later (fig. 3).

The injection head 3 of the soldering apparatus 1 is disposed below the printed circuit board 40, and the printed circuit board 40 is disposed on the support 2 of the soldering apparatus 1. A lower surface portion 42k of the lower surface 40k of the printed board 40, which is a solder point, is exposed downward from the opening of the support base 2.

As shown in fig. 1, the injection head 3 is provided perpendicularly to the printed board 40, and there are cases where the injection port 4 of the injection head 3 is provided toward the lower surface 40k of the printed board 40 (first embodiment) and cases where it is provided obliquely to the printed board 40 as shown in fig. 11 (second embodiment).

The injection head 3 has a substantially cylindrical or square tubular shape, and a laser introduction tube 5 projects from a side surface thereof at a right angle. An optical fiber 8 leading to a semiconductor laser or the like is connected to the laser introduction cylinder 5, and the laser light L output from the semiconductor laser or the like is guided to the inside of the emission head 3 through the optical fiber 8. Inside the injection head 3, an optical component 6b such as a half mirror 6a for changing the direction of the introduced laser light L and an optical lens for condensing the laser light L to a predetermined diameter at a pad lower surface portion 42k as a brazing point is built in the optical path to the injection port 4.

As described above, the injection port 4 is provided at the upper end of the injection head 3 and faces the lower surface 40k of the printed board 40. The laser light L incident on the injection head 3 is injected from the injection port 4 toward the pad lower surface portion 42k as the brazing point P by the internal optical system 6. The ejection port 4 is provided with a transparent cover glass 7 as a whole and a center output limiting glass 7a provided as needed as described later.

There are two types of laser light L emitted from the emission port 4 toward the pad lower surface portion 42k as the solder joint P. The first is a case where the cross section of the pad lower surface portion 42k as the irradiation surface is the same output level as a whole (fig. 1, 9(b)), and the second is a case of a double ring structure in which the central portion L1 and the outer peripheral portion L2 concentrically arranged therearound surround the central portion L1 (fig. 2, 10 (b)). In this case, in the latter case, the output level of the outer peripheral portion L2 is set to be greater than the output level of the central portion L1.

In fig. 2, the laser light L of the latter double ring structure is shown, and the central portion L1 is shown in light black.

Although fig. 10 shows the laser light L of uniform output obliquely arranged, the laser light L of uniform output may be used, although not shown.

When the laser light L has a uniform output as in the former case, since the optical system 6 is not subjected to a process of reducing the output level of the central portion L1 of the laser light L, the laser light L incident on the emission head 3 passes through the optical system 6 of the emission head 3 and the protective glass 7 as it is, and becomes the same output level in the entire cross section of the irradiation surface as described above. Fig. 9(b) shows a schematic diagram of the output level in this case. In any case where the irradiation range of the uniform output laser light L is irradiated in a vertical or inclined state, the irradiation range is set as the pad lower surface portion 42k as described later.

When the laser light L having a high uniform output level (B) equal to or higher than the melting temperature of the solder wire) is vertically arranged and continuously irradiated to the protruding end of the lead wire 52 during the preheating period, the protruding end may be overheated to cause discoloration called "lead burn", and therefore, as described later, the output of the laser light L is controlled so as not to cause "lead burn".

When the laser light L having a strong uniform output level is obliquely provided and the laser light L is obliquely irradiated to the solder joint P, the irradiated surface expands into an elliptical shape as shown in fig. 12, and the output level is slightly lower than in the case of being vertical. In this case, output control is also performed as needed without causing "lead burn".

On the other hand, when the laser light L is the latter laser light L of an unequal output, a member (not shown) for limiting the output level of the central portion L1 of the laser light L is provided at an arbitrary portion of the optical system 6 of the emission head 3, or, as shown in fig. 2, a central portion output limiting glass 7a having an output limiting region 7b for limiting the output level of the central portion of the laser light L is provided along the upper side of the protective glass 7. In this case, in the case where the output level of the outer peripheral portion L2 is 100, the output level of the central portion L1 is limited to 40 ~ 60. The output level is changed by replacing the center portion output limiting glass 7a with a glass having various limiting values.

In addition, the diameter of the central portion L1 of the laser light L of unequal output is the largest of the inner diameter of the through hole 41. Thus, since the output level of the central portion L1 irradiated to the protruding end of the lead 52 inserted through the through hole 41 is much weaker than the peripheral portion L2 therearound, even if the laser light of the weak central portion L1 is continuously irradiated in the preheating process, "lead burn" does not occur.

The laser light L having such unequal outputs may be vertically or obliquely arranged.

In the case where the laser light L of the unequal output is vertically arranged, the outer peripheral portion L2 is an annular region obtained by subtracting the center portion L1 located at the center portion from the irradiation range of the laser light L covering the pad lower surface portion 42k as the solder joint P. When the pad lower surface portion 42k of the printed board 40 is circular, the laser light L is irradiated to the entire pad lower surface portion 42k to reach the outer edge of the pad lower surface portion 42k with the maximum diameter. (the shape of the pad lower surface portion 42k of the printed board 40 is not limited to a circular shape, and various shapes are available, for example, in the case of an oval, the range is the short side width so as not to irradiate the substrate main body 40a as an insulator with the laser light L.)

When the laser light L of the unequal output is obliquely arranged, the irradiation surface is elliptical as shown in fig. 12, and therefore, the laser light L is irradiated in a range such that the long axis side thereof does not go beyond the pad lower surface portion 42 k.

A protection nozzle 20 is attached to the ejection port 4 of the ejection head 3 above the protection glass 7 (or the center portion output regulating glass 7 a). The protection nozzle 20 has a hollow conical shape extending upward from the injection port 4, and a cylindrical nozzle port 21 is fitted into a tip end portion thereof. The nozzle opening 21 is formed of a heat-resistant material such as ceramic, for example. The nozzle opening 21 is formed with a through hole 22 through which the laser light L narrowed to be thin passes. The through hole 22 is slightly larger than the diameter of the laser light L passing through the portion.

A heated gas supply pipe 26 is connected to the base of the protection nozzle 20 near the injection port 4 of the injection head 3, and high-temperature gas is supplied to the inside all the time. The high-temperature gas may be ordinary air or an inert gas such as nitrogen. The melting point of the solder wire 15 varies depending on the composition, but is about 220 ℃ in the case of lead-free solder. The temperature of the high-temperature gas supplied to the protective nozzle 20 is such that the through hole 41 and the periphery thereof or the solder wire 15 supplied to the part can be preheated (for example, 110 to 150 ℃) and does not exceed the temperature of the solder wire 15 immediately before the melting point is reached at most. Then, the high-temperature gas is blown upward from the through hole 22 as hot air N. The inside of the protection nozzle 20 is always kept at a positive pressure by the supplied high-temperature gas. Therefore, the foreign matter (fine product) C does not enter the protection nozzle 20 from the through hole 22.

The protection nozzle 20 may be simply a conical hollow cylinder (not shown), but fig. 2 and 3 show an example in which a conical guide wall 24 is provided along the inner circumferential surface of the protection nozzle 20.

The guide wall 24 forms a guide flow path G for guiding the flow of the hot air N between the inner circumferential surface of the protection nozzle 20 and the guide wall 24. If the gap between the inner peripheral surface and the guide wall 24 is gradually narrowed toward the through hole 22, the flow velocity of the hot air N flowing through the guide flow path G can be increased. In addition, since the guide wall 24 covers the upper surface of the cover glass 7 (or the central portion output limiting glass 7a), the high-temperature gas blown into the protection nozzle 20 is prevented from contacting the cover glass (or the central portion output limiting glass 7 a).

The heated gas supply pipe 26 may be connected to the base of the protection nozzle 20 at a right angle, but may be connected to the protection nozzle 20 in a tangential direction of the inner peripheral surface of the protection nozzle 20 as shown in fig. 4, and the blown high-temperature gas forms a spiral flow along the inner peripheral surface (or the guide flow path G) in the protection nozzle 20 and is ejected as hot air N of a fine spiral flow from the through hole 22. By forming the hot air N into a spiral flow, the directivity of the ejection direction can be improved, and the lead 52 and the land 42 disposed close to the through hole 22 can be intensively preheated at the time of soldering.

Further, although the preheating is performed by the hot air N from below the printed circuit board 40, the preheating may be performed by the hot air N from above the printed circuit board 40.

In the present embodiment, the exhaust duct 30 is provided so as to surround the periphery of the through hole 22 of the protection nozzle 20. The exhaust duct 30 is provided as required, and is not essential. Here, an example in which the exhaust duct 30 is provided is shown.

The exhaust duct 30 is a disk-shaped member, and has an opening 31 at the center, and the upper end portion (nozzle opening 21) of the protection nozzle 20 is inserted into the opening 31. The upper edge 30a of the exhaust duct 30 and the upper end of the nozzle opening 21 of the protection nozzle 20 are located below the lower surface 40k of the printed circuit board 40 located above, and a gap is formed therebetween.

The gap is formed to have a width exceeding the amount of protrusion of the lead 52 from the lower surface 40k of the printed board 40. Thus, even if injection head 3 moves relative to printed circuit board 40 together with exhaust duct 30 at the end of soldering, upper edge 30a of exhaust duct 30 and the upper end of nozzle opening 21 do not come into contact with the protruding end of soldered lead wire 52.

An exhaust cylinder portion 32 is provided on a side wall of the exhaust duct 30, and an exhaust pipe 33 is connected to the exhaust cylinder portion 32. The exhaust pipe 33 always sucks and discharges air in the exhaust duct 30.

The hot air N discharged from the through hole 22 of the nozzle opening 21 of the protection nozzle 20 collides with the lower surface 40k of the printed circuit board 40 (the lead wire 52, the through hole 41, and the periphery thereof in the case of soldering), preheats the colliding portion, and then flows into the exhaust duct 30. Most or all of the hot air N flows into the exhaust pipe 33.

Accordingly, most or all of the air in the exhaust pipe 30, fumes generated during soldering and scattered in the air, and fine products C such as solder beads are discharged from the exhaust pipe 33.

An annular cooling pipe 35 is provided on the outer periphery of the trunk portion of the protection nozzle 20, and a cooling water supply pipe 36 and a cooling water discharge pipe 37 are attached to the cooling pipe 35. The cooling water is supplied from the cooling water supply pipe 36, circulated in the cooling pipe 35, returned to the cooling water discharge pipe 37, and discharged therefrom. The protective nozzle 20 is thereby cooled by the cooling water.

The solder wire feeder 11 is used to feed the solder wire 15 wound around a pulley (not shown) toward the pad lower surface portion 42k of the pad 42 as a solder point by a required amount each time when necessary. The solder wire feeder 11 has a lead nozzle 12 extending to the vicinity of the lower pad surface portion 42k as a solder point. The solder wire feeder 11 receives control commands such as the timing and amount of feeding the solder wire 15 from the control device during the soldering operation, and discharges the solder wire 15 from the pilot nozzle 12 in accordance with the control commands. The solder wire 15 that has been paid out is supplied to a position where it contacts the lead 52 or the pad lower surface portion 42k that is a solder point, or a position where it contacts both. At this time, as will be described later, the tip portion of the solder wire 15 that is fed out is preheated by being exposed to only the hot air N or the hot air N and the laser light L, but the heating temperature of the hot air N and the output level of the laser light L are low, and melting does not occur at this time.

The solder wire 15 is generally circular in cross-sectional shape, but as shown in fig. 1 and 3, the solder wire 15 may be flattened into a flat shape by a pair of upper and lower press rollers 13 before being inserted into the guide nozzle 12, and

flat portions

16a and 16b may be provided on the front and back sides of the solder wire 15. In this case, the guide nozzle 12 also forms the guide hole into a flat oval shape corresponding to the solder wire 15, and supplies the flat surface portion 16a on one side of the flat solder wire 15 along the lower surface 40k of the printed board 40. This causes the laser beam L to irradiate the flat surface portion 16b on the opposite side, thereby reducing scattering of the laser beam L and facilitating absorption by the flat solder wire 15.

During soldering or during preheating and soldering, an oscillation control command is issued from a laser controller, a semiconductor laser or the like which has received the command emits laser light L at a predetermined output and irradiation time, and the emission head 3 emits the laser light L toward the solder joint, i.e., the lower pad surface portion 42k, vertically or obliquely upward from below. Then, the soft solder wire 15 is supplied thereto.

In either case, in principle, the feeding of the soft solder wire 15 is completed before the laser light (uniform-non-uniform output) L of the output level (B) is emitted.

Thus, when soldering, the solder wire 15 is heated and melted by the laser light L, and soldering is performed.

A CCD camera 9 is attached to the lower end of the emission head 3, the optical axis of the CCD camera 9 coincides with the laser beam L, and the brazing spot can be imaged by the CCD camera 9 through the emission port 4. The image of the solder joints captured by the CCD camera 9 is displayed on the monitor 10 via the control device.

Before soldering, the alignment of the laser beam L with respect to the pad lower surface portion 42k of the solder joint can be performed while observing the image displayed on the monitor 10 using the CCD camera 9, or the state of the soldering operation of the solder joint can be observed by the CCD camera 9 at the time of the soldering operation.

Next, the operation of the soldering apparatus 1 of the present invention will be described. The laser soldering method according to the present invention includes a first embodiment (fig. 1 to 8: vertical arrangement) and a second embodiment (fig. 11: inclined arrangement).

The first embodiment is a case where the injection head 3 is vertically provided on the lower surface 40k of the printed substrate 40, and the second embodiment is a case where the injection head 3 is inclined at an inclination angle θ with respect to a vertical line of the lower surface 40k of the printed substrate 40. The inclination angle theta is 50 DEG + -10 deg.

As described above, there are two cases, that is, the case where the laser light L is emitted at a uniform output level and the case where the laser light L is emitted at an unequal output level.

In the soldering step, as shown in fig. 9(a) and 10(a), there are cases where the laser output is changed in stages: a first output step ((1) (2) (3) (4) (5) (6) (7)) of continuously changing the laser output: a second output step ((20) (4) (21)) of outputting in a rectangular shape: and a third output step ((10) (4) (5)).

In the first output step, the output is set to two stages, i.e., level (a) and level (B), but the present invention is not limited thereto, and a plurality of stages may be used. In this case, although preheating is possible at level (a), the output level is such that "lead burn" (output in which the temperature of the irradiated portion is raised to a level of about 110 to 150 ℃) does not occur, and level (B) is such that "soldering" (output at a temperature equal to or higher than the solder melting temperature) is possible.

The first to third output steps are determined by the conditions of the object to be soldered, and the timing of switching is determined by software input to the controller or by detecting the measured temperature of the solder joints using a radiation thermometer (not shown).

As for the preheating of the brazing point P, there are two cases, one is preheating with only the hot air N without the laser L, and the other is preheating by the cooperation of the hot air N and the laser L.

(soldering work of the first embodiment (vertical))

Hereinafter, a soldering operation in the first embodiment (vertical) using the laser light L of uniform output or the laser light L of non-uniform output will be described (fig. 1, 2 to 8, 9, and 10).

The optical axis of the injection head 3 is aligned with the center of the through hole 41 of the printed circuit board 40 to be soldered provided on the support 2 of the soldering apparatus 1. The ejection head 3 is disposed below the print substrate 40 and perpendicular to the print substrate 40. The optical axis alignment is performed automatically by image processing or manually by adjustment via the monitor 10.

Before the optical axis alignment is completed, the hot air N ejected from the through hole 22 is blown to the vicinity of the pad lower surface portion 42k of the soldering point P to heat the portion. At this time, the laser light L is not emitted.

The first output step (FIGS. 9(a) and 10 (a): (1) to (7))

Preheating process (preheating by hot wind N and laser L)

As described above, when the optical axis mating ends, the through hole 22 is located directly below the pad lower surface portion 42k of the solder joint P. At this time, the hot air N ejected from the through hole 22 preheats the through hole 41 and its surroundings, and the lead 51 inserted into the through hole 41. Simultaneously with or after the completion of the alignment of the optical axes, the laser light L (indicated by (1) in fig. 9 a and 10 a) is emitted to the lower surface portion 42k of the pad and the lead 52, which are output uniformly or non-uniformly.

In the case of the laser light L of uniform output, if the output level is high, a "lead burn" phenomenon occurs in which the lead 52 is overheated and the irradiated portion is discolored, and therefore, at this time, the output (indicated by level (a)) is lowered to such an extent that the "lead burn" phenomenon does not occur. At this output level (a), the preheating temperature based on the hot air N and the laser output is a temperature (for example, 110 to 150 ℃) lower than the melting point of the solder wire 15 used.

In the case of the laser light L of the uneven output, the output level of the outer peripheral portion L2 is set to (a) so that the solder wire 15 fed to the soldering point P is not melted. Since the output level (B) of the center portion L1 is low compared to the outer peripheral portion L2, it is sufficient to manage the output level of the outer peripheral portion L2.

When the hot air N is not a spiral flow but is ejected perpendicularly from the through hole 22 toward the through hole 41, the periphery of the pad lower surface portion 42k around the center, the inner peripheral surface of the through hole 41, and the lead 52 inserted through the through hole 41 are preheated as described above, and the pad upper surface portion 42j and the vicinity thereof are preheated by the hot air N bypassing the upper surface 40j of the printed board 40 through the through hole 41. This is the same in the soldering step described later.

When the hot air N spirally winds up and is discharged toward the through hole 41, the hot air is blown into the through hole 41 with a higher discharge directivity than the case of discharging only as described above, and the lead wire 52 existing at the center of the through hole 41 is mainly preheated. Most of the hot air N colliding with the through hole 41 including the lead wire 52 flows directly to the surroundings, and preheats the pad lower surface portion 42 k. The hot air N passes through the remaining portion of the via hole 41 to preheat the pad upper surface portion 42j and its vicinity. This is also the same as the soldering step described later. The preheating time is determined by setting a time from the end of the optical axis alignment or measuring the temperature of the preheating portion using a radiation thermometer.

Soldering Process

When the preheating is performed as described above, the preheating step is switched to the soldering step as the preheating step is completed, and the output of the laser beam L having a uniform output is switched to the horizontal level (B). The output of the outer peripheral portion L2 is switched to the horizontal (B) for the laser light L of the unequal output.

The feeding of the solder wire 15 is performed before the output of the laser light L (or the outer peripheral portion L2) is switched to the level (B).

When the solder wire 15 comes into contact with the lead 52 (or the pad lower surface portion 42k), the laser light L (or the outer peripheral portion L2) of the level (B) is output, and the solder wire 15 is rapidly melted from the irradiated portion including the contact portion. When the solder wire 15 changes from the solid phase to the liquid phase, latent heat is required, and therefore the temperature of the molten solder 15m slightly decreases, but the molten solder remains in the liquid phase due to heat from the laser L. The solder wire 15 is continuously supplied to the soldering point P immediately before the end of soldering, and is continuously melted.

During the soldering step, as described above, the amount of the molten solder 15m is increased by supplying the solder wire 15, and the molten solder is spread over the lead 52 and the pad lower surface portion 42k to connect the two, and is raised in the direction of the upper surface 40j of the printed circuit board 40 through the gap S between the two preheated by the "capillary phenomenon", so that the pad upper surface portion 42j of the printed circuit board 40, the lead 52, and the gap S therebetween are filled with the molten solder 15 m.

As described above, since the entire through hole 41 and the lead 52 are preheated, the molten solder 15m does not solidify, and the above-described "capillary phenomenon" occurs while maintaining a liquid phase (fig. 6).

In addition, when the cross section of the solder wire 15 is circular, the laser light L is scattered around when it is irradiated on the outer surface, and the energy absorption efficiency is deteriorated, but when the solder wire 15 is flattened into a flat shape by the pinch roller 13 before being supplied, the amount of scattering around is reduced when the laser light L is perpendicularly irradiated on the one flat surface portion 16b, and the solder wire 15 is melted faster than the circular solder wire 15.

In the soldering step, since soldering is performed from below the printed circuit board 40, mist generated when the solder wire 15 melts or fine products C such as fine solder beads scattered when the solder wire 15 melts may be scattered around the soldered portion, but these are blown off by the hot air N ejected from the through hole 22 of the protection nozzle 20 and do not enter the protection nozzle 20. Thus, even if soldering is performed from below the printed board 40, the cover glass 7 of the head 3 is not contaminated. (since the fine product C is blown around as long as the hot air N is appropriate and does not adhere to the protective glass 7 of the injection head 3, the protective nozzle 20 may not be provided in this case.)

The mist and other fine products C blown off by the hot air N are received by the exhaust duct 30, and are discharged to the outside through the exhaust pipe 33, and the exhaust duct 30 is provided so as to surround the protection nozzle 20, and the inside is maintained in a negative pressure state. In the exhaust duct 30, as described above, the negative pressure is always maintained by the exhaust gas from the exhaust pipe 33, and the external air flows into the inside from the gap between the printed circuit board 40 and the upper edge of the exhaust duct 30, so that the leakage of the fine product C out of the exhaust duct 30 due to the soldering work is greatly suppressed. This prevents the solder from below the printed circuit board 40 from contaminating the surrounding environment.

In the conventional soldering using the laser beam L from above the printed circuit board 40, the fine product C flying upward may fall onto the printed circuit board 40 with the passage of time, but this does not occur in the soldering from below as in the present invention.

In the soldering step described above, the laser light L of uniform output at the high output level (B) continues to irradiate the tip end portion of the lead wire 51, but the heat applied to the lead wire 51 by the laser light L is absorbed by the continuously melted solder wire 15m, and the temperature rise is suppressed, so that "lead burn" does not occur.

In contrast, in the case of the laser light L of an unequal output, since the output level of the central portion L1 at this time is a low level (a) to the extent that the solder wire 15 does not melt, even if the distal end portion of the lead wire 51 is continuously irradiated as described above, the "lead burn" does not occur.

Post-heating step

When soldering of through hole 41 and lead 52 is completed, laser light L is directly blocked (step (5)). Then, the injection head 3 is moved to the next soldering point P, and the preheating and soldering work is performed at the destination.

As described above, when the laser light L is interrupted immediately after the soldering is completed (step (5)), the solder 15h being solidified is rapidly solidified by the interruption of the laser light L even if heated by the hot air N until the solder moves to the next soldering point P. Therefore, strain (or peeling) may occur in the solder-attached portion due to rapid cooling. Therefore, it is preferable to decrease the output level of the laser light L in stages from the soldering end time (steps (6) and (7)). In the case of lowering the output stepwise, there are 2 steps in the figure, but there may be a plurality of steps.

As a result, it is preferable to form the solidified solder 15h having a conical shape as shown in fig. 8 on the front and back surfaces of the printed circuit board 40.

The second output step (20, 4, 21, shown by the single-dot chain line arrows in FIGS. 9(a) and 10 (a))

(preheating step: use of laser together with Hot air)

In the preheating step, heating of hot air N and heating of laser light L by uniform or non-uniform output are performed at the soldering point P. After the completion of the alignment of the optical axes, the laser light L is continuously increased until the start of soldering. The output level of the outer peripheral portion L2 of the laser light L of uniform output or of non-uniform output at the time of starting soldering is (B). In addition to the above, the description of the first output step is applied.

(soldering Process)

The first output step is applied because the soft solder wire 15 is supplied and soldering is performed, as in the first output step.

(post-heating step)

The output of the laser light L is gradually reduced at the same time when soldering is completed. This can avoid rapid cooling of the molten solder 15m and relax the strain of the solidified solder 15 h. In addition to the above, the description of the first output step is applied.

A third output step (FIGS. 9(a) and 10 (a): dotted arrows (10) (4) (5)/(6) (7))

(preheating step: Single preheating with Hot air)

In the preheating step, heating by separate heating with hot air N is performed at the soldering point P without emitting the laser light L. In this case, after the termination alignment is completed, the process proceeds to the start of soldering after a predetermined time of warm-up time has elapsed (or when the temperature measured at the soldering point P by the radiation thermometer reaches the soldering start temperature).

(soldering Process)

(post-heating step)

As in the first output step, the laser beam L is interrupted at the same time as the soldering is completed. Alternatively, the output is lowered stepwise. Here also the same as the first output step, so the first output step is applied. (of course, slow cooling in a subsequent step that is the second output step may be used) in addition to the above, the description of the first output step is cited.

Next, the soldering operation of the second embodiment will be explained. As described above, in the second embodiment, the ejection head 3 is provided obliquely to the vertical line of the print substrate 40. Therefore, in this case, the optical axis of the injection head 3 is aligned with the protruding base optical axis of the lead 51 protruding from the through hole 41. In the second embodiment, this state is referred to as "optical axis alignment".

The feeding direction of the solder wire 15 is preferably a direction not to be a shadow of the lead 52 and not to interfere with the tip of the protection nozzle 20. The shaded portions are indicated by light black (fig. 12). In fig. 12, the solder wire 15 is fed at an angle of 140 ° with respect to the optical axis of the laser light L, but is of course not limited thereto.

When the laser light L is incident on the solder joints P obliquely to the vertical line of the printed circuit board 40, the irradiated surface describes an elliptical shape (fig. 12). When the laser light L is output uniformly, strictly speaking, as shown in fig. 9(b), the output is not uniform over the entire surface of the irradiation surface, but the center portion is strong and the outer edge portion is slightly weaker than the center portion for optical reasons.

As described above, when the solder joints P are irradiated so that the optical axis is aligned with the protruding base portions of the leads 51, the solder wire 15 is rapidly melted, flows to the leads 52 and the pad lower surface portions 42k, and covers them.

After the laser light L emission is started, the protruding portion of the lead 52 is irradiated with the laser light L at the strong level (B) for a minute time before the coating, but as described above, even if the laser light L is uniformly output, the output level of the outer edge portion thereof is low, and therefore, if the laser light L is irradiated for a minute time before the coating, the "lead burn" does not occur.

In contrast, in the case where the laser light L is of an unequal output, as described above, the output level of the center portion L1 is low compared to the outer peripheral portion L2. The protruding portion of the lead 52 is irradiated with the central portion L1 where the output level is low, and therefore, of course, no "lead burn" occurs. The solder wire 15 is irradiated with the outer peripheral portion L2 having a high output level and is melted.

Other points are the same as those of the first embodiment, and therefore the description of the first embodiment is applied.

Description of reference numerals

1: a soldering device; 2: a support table; 3: an ejection head; 4: an ejection port; 5: a laser introduction cylinder; 6: an optical system; 6 a: a semi-transparent semi-reflective mirror; 6 b: an optical component; 7: protecting glass; 7 a: a central portion output limiting glass; 8: an optical fiber; 9: a CCD camera; 10: a monitor; 11: a solder wire supply unit; 12: a pilot nozzle; 13: a compression roller; 15: a soft solder wire; 15 h: a solidified soft solder; 15 m: melting the soft solder; 16a, 16 b: a planar portion; 20: protecting the nozzle; 21: a nozzle opening; 22: through holes; 24: a guide wall; 26: a heating gas supply pipe; 30: an exhaust duct; 30 a: an upper edge; 31: an opening part; 32: an exhaust cylinder section; 33: an exhaust pipe; 40: a printed substrate; 40 a: a substrate body; 40 j: an upper surface; 40 k: a lower surface; 41: a through hole; 42: a pad; 42 j: a pad upper surface portion; 42k is as follows: a pad lower surface portion; 42 n: an inner edge; 43: a conducting portion; 50: an electronic component; 51: a lead wire; c: a fine product; g: a guide flow path; l: laser; l1: a central portion; l2: an outer peripheral portion; n: hot air; s: a gap.

Claims

1. A laser soldering method for melting a solder wire supplied to a through hole of a printed board by a laser beam and soldering a lead wire inserted through the through hole of an electronic component mounted on an upper surface side of the printed board to a pad provided in the through hole,

the laser light is irradiated perpendicularly or obliquely from below with respect to the pad at the soldering point,

spraying hot air from below the printed circuit board to the pad and the lead protruding downward from the through hole to preheat the pad and the lead,

simultaneously with or after the start of the preheating, supplying a solder wire from below the printed circuit board to a position in contact with either the pad or the lead while irradiating the pad and the lead with a laser from below the printed circuit board,

subsequently, the supplied solder wire is melted by a laser, and the pad and the lead are connected by the melted solder,

then, the supply of the solder wire is stopped, and at the same time as or after the stop of the supply of the solder wire, the irradiation of the laser is stopped to solidify the molten solder.

2. Laser soldering method according to claim 1,

using laser light whose output level is equal over the entire cross section of the irradiation face,

the output level during preheating is made to be a preheating level below the melting temperature of the solder wire,

the output level during soldering is made to be a melting level equal to or higher than the melting temperature of the solder wire.

3. Laser soldering method according to claim 1,

preheating is performed based on hot air only during preheating,

at the start of soldering, a laser beam is emitted to an output level equal to or higher than the melting temperature of the solder wire.

4. Laser soldering method according to claim 1,

emitting laser at the beginning or in the middle of preheating to gradually increase the output level from zero to a melting level above the melting temperature of the solder wire,

5. Laser soldering method according to claim 1,

using a laser light whose output level of a cross section of an irradiation surface is higher at an outer peripheral portion thereof than at a central portion thereof,

the output level of the central portion is below the melting temperature of the solder wire,

the output level of the outer peripheral portion is higher than the melting temperature of the solder wire,

the central portion is set to irradiate the inside of the through hole of the pad,

6. Laser soldering method according to claim 1,

preheating is performed based on hot air only during preheating,

7. Laser soldering method according to claim 1,

8. A laser soldering apparatus for soldering a lead of an electronic component to a pad of a printed circuit board by laser, characterized in that,

the laser soldering apparatus includes:

a support table that supports a printed circuit board on which the electronic component is mounted on an upper surface thereof, the lead of the electronic component protruding downward from a through hole of the printed circuit board;

an ejection head which is provided vertically or obliquely to the printed board below the printed board and ejects laser light vertically or obliquely toward the pad;

a solder wire supply unit for supplying a solder wire to a position where the solder wire is in contact with either the pad or the lead during soldering;

a hollow protection nozzle provided at an ejection port of the ejection head, extending from the ejection port toward an upward printed board, and having a through hole at a distal end facing the printed board; and

and a heated gas supply pipe provided in the protective nozzle, for supplying heated gas to the protective nozzle to eject hot air from the through hole toward the printed circuit board.

9. Laser type soldering device according to claim 8,

an exhaust duct is further provided at a position facing the through hole of the protection nozzle, and an upper surface of the exhaust duct facing the lower surface of the printed circuit board is open.

10. Laser type soldering device according to claim 8,

the output level of the central portion is set to be equal to or lower than the melting temperature of the solder wire, and the output level of the outer peripheral portion is set to be equal to or higher than the melting temperature of the solder wire.

11. Laser type soldering device according to claim 8,

the protective nozzle is formed so as to be reduced in diameter toward the through hole,

inside the protection nozzle, a guide wall for guiding hot air is provided along an inner circumferential surface of the protection nozzle.